Abstract

Stratigraphy of the bunter in the SW margin of the Fore-Sudetic Monocline

The stratigraphy of the Bunter from 3 borehole profiles in the SW margin of the Fore-Sudetic monocline is here described on the basis of megaspores and the cyclic sequence of lithological assemblages. Two index megaspore· assemblages have been differentiated, viz. the Otynisporiteseotriassicus, characteristic of the lower oolithic beds of the Lower Bunter, and Trileites validus, an index assemblage of the Röt. The absence of megaspores associated with the megaspore assemblage I (Fuglewicz 1973a) and the mode of development of the deposits here under consideration suggest the existence of a stratigraphic lacuna involving the upper oolithic beds and the supra-oolithic Bunter beds.

The object of the present paper is to describe the stratigraphy of the Bunter in the SW margin of the Fore-Sudetic monocline, as based on megaspores and the cyclic sequence of lithological assemblages. The stratigraphic division of the deposits here considered is that accepted by Fuglewicz (1973a). The material needed for the investigation work has been obtained from 3 boreholes drilled· by the Geological Institute: Przesieczna 1, Stęszów IG-1 and Czerńczyce IG-1.

Sub-oolitic, lower-oolitic and inter-oolitic Bunter beds have been differentiated within the. profiles under consideration, while the Röt is observed to consist of sub-gypsum, lower gypsum, inter-gypsum, upper-gypsum and supra-gypsum beds. The occurrence· of megaspores has been observed in the lower-oolitic beds of the Bunter and in the Röt deposits. The megaspore assemblage from the lower-oolitic beds, the first to be worked out, is the oldest one so far reported from the Bunter. The Otynisporites eotriassicus assemblage consists· of three megaspore species: Trileites vulgaris Fugl. the predominant Otynisporites eotriassicus Fugl. and Hughesisporites simplex Fugl. The megaspore assemblage occurring in the Röt, previously differentiated by the writer as the megaspore assemblage II (Fuglewiczb1973 a), has now been assigned the name of Trileites validus Fugl. This assemblage consists of 6 megaspore species. Trileites validus Fugl. is the predominant one, Narkisporites brevispinosus Fugl. is less numerous while Bacutriletes insolitus Fugl., B. asuphus Fugl., Narkisporites sp., Dijkstraisporites sp., Erlansonisporites licheniformis Fugl. and Aneuletesrotundus Fugl. occur sporadically.

Comparisons of the Bunter megaspore assemblages supplemented by the writer's observations lead to the conclusion that the occurrence of some species is distinctly connected with facial development. In the marine (Röt) deposits the dominance is observed of the smooth megaspores (Trileites validus Fugl.), while ornamented megaspores as a rule predominate in the limnic sediments (comp. the olenekian mega-spores of NE Poland (Fuglewicz 1973a).

The absence of megaspores contained in the megaspores assemblage I (Fuglewicz 1973a), also the facial analysis of the Bunter deposits here considered, suggest a stratigraphic lacuna (Hardegsen disconformity) in the analyzed profiles involving the Middle Bunter (upper-oolitic and supra-oolitic beds).